Optical Vortices Sharp Focusing by Silicon Ring Gratings Using High-Performance Computer Systems

The diffraction of vortex laser beams with circular polarization (with different direction of polarization rotation) by silicon ring gratings was investigated in this paper. The silicon diffractive axicons with different numerical apertures (NA) were considered as such ring gratings. The considered diffractive axicons are compared with single silicon circular protrusion (cylinder). The finite difference time domain method was used for Light propagation (3D) through the proposed silicon ring gratings and silicon cylinder. The possibility of subwavelength focusing by varying the height of the elements is demonstrated. In particular, it is numerically shown that a silicon cylinder forms a light spot with the minimum size (intensity) of the longitudinal component of the electric field FWHM is 0.32λ.